Optimization of semiconductor devices continues to be an important goal for the semiconductor industry. The continued miniaturization of semiconductor devices, such as bipolar transistors, presents ongoing challenges to semiconductor manufacturers in maintaining or improving overall device performance. One such example resides in the problems associated with defects, such as collector-emitter (CE) pipes, which is a short-circuit between the collector and emitter. Defects can occur in the collector of a bipolar transistor as the result of a boron implantation step. In many designs, boron is used as the dopant to impart the required degree of conductivity to the collector. This is achieved through the implantation of boron that is typically conducted at a medium energy and at medium to high doses. This type of implant can, unfortunately, lead to a high density defects or threading dislocations that give rise to CE pipes. The boron collector implant creates a region of defects near the range of the implant. The implantation is typically followed by an anneal, and the implanted boron is subjected to thermal budgets associated with subsequent processing steps. During these thermal processes, boron can readily diffuse along the length of the dislocations and diffuse into the silicon adjacent to the dislocations. The dislocations act like pipes or soaker hoses that carry boron along the dislocations and into the silicon adjacent to it. The boron atoms can easily diffuse to such an extent and create a conductive path between the emitter and the collector. If the dislocations extend between the collector and emitter, in particular, through the n-type base region, the pipes will create thin p-type regions through the n-type base, which shorts between the collector and emitter and leads to a defective device. In turn, reliability and yields are significantly reduced.
To address this issue, the semiconductor manufacturing industry has attempted to reduce the number of defects by reducing the boron dose. Unfortunately, this can affect device performance in that the collector substrate becomes less conductive and more resistive, which can reduce device speed and overall performance. Alternatively, the semiconductor manufacturing industry has also attempted to implant a shallow, high density layer, and then epitaxially grow silicon on it. This approach is inherently expensive because it requires an additional mask for the buried layer implant and additional epi step.
Accordingly, there is a need to provide a process and device by which dislocations or defects in bipolar devices can be reduced without sacrificing device performance and significantly increasing production costs.